Thirst and body water

Question 1

How does water lose the body?

Answer 1

Via kidneys, lungs, skin, faeces and sweat

Question 2

How is water input into the body?

Answer 2

Drink and metabolic water

Question 3

What receptors stimulate thirst?

Answer 3

Osmoreceptors in the hypothalamus

Question 4

What is Hyposthenuria and what does it suggest?

Answer 4

Urine with low specific gravity

Suggests increased loss of water without increased loss of solute eg. polyuria and diabetes

Question 5

What is Hypersthenuria and what does it suggest?

Answer 5

Urine with a high specific gravity

If persistent, suggests loss of solutes without water. DEHYDRATION

Question 6

What is the urine specific gravity of cats and dogs?

Answer 6

USG of 1.035

Question 7

What causes blood ADH to increase?

Answer 7

Hypovolaemia (decrease atrial filling pressure)
Hypotension (baroreceptor mediated)
Dehydration (osmolarity increases)
Angiotensin II 
Increase in sympathetic activation

Question 8

ADH acts to….

Answer 8

to preserve blood volume
to prevent a diuresis
to prevent a natriuresis

Question 9

What receptors does ADH activate to insert aquaporins?

Answer 9

V1 and mainly V2

Question 10

How do aquaporins work?

Answer 10

4 proteins inserted in epithelial membranes

Create a hydrophilic pore to allow water to pass through a hydrophobic membrane (lipid bilayer)

Question 11

What are the two most important aquaporin?

Answer 11

AQP1 in apical and basolateral membrane of PT. Allows isosmotic removal of water (and solutes). By end PT, 65% volume reduced.
AQP1 is main relevant channel in descending loop of Henle (water loss from tubule) and is ADH responsive

Question 12

What is the normal water intake/ urine volume and urine osmolality for a dog?

Answer 12

Intake: 90ml/kg

Question 13

What is the normal water intake/ urine volume and urine osmolality for a cat?

Answer 13

Intake: 45ml/kg

Question 14

What is the normal water intake/ urine volume and urine osmolality for a cow?

Answer 14

Intake: 100ml/kg